(a) Field of the Invention
The present invention relates to a forward/reverse control system for a continuously variable transmission, and more particularly, to a forward/reverse control system for a continuously variable transmission that simplifies a structure of a hydraulic circuit of the system.
(b) Description of the Related Art
A belt-type continuously variable transmission for vehicles generally includes a continuously variable shifting unit for performing continuous shifting using a drive force transmitted through a torque converter, and a forward/reverse control system for controlling a drive direction of the vehicle. The forward/reverse control system includes a planetary gearset for controlling the forward/reverse control system, and a forward clutch and a reverse clutch for controlling elements of the planetary gearset such that the drive direction of the vehicle is controlled to either forward or reverse.
With reference to FIG. 1, a power clutch 1 and a reverse brake 3 are selectively controlled to engaged and disengaged states by a forward/reverse control system such that a drive direction of the vehicle is controlled to forward or reverse. In such a forward/reverse control system for a continuously variable transmission, line pressure is supplied to or exhausted from the forward clutch 1 and the reverse brake 3 through hydraulic lines selectively formed by control of a N-D control valve 14 and a N-R control valve 12 according to an On and Off operation of a clutch control solenoid valve 5, and it is formed by control of a manual valve 11 according to a range selection of a shift lever.
A forward clutch accumulator 13 and a reverse brake accumulator 15 are provided on hydraulic lines connected respectively to the forward clutch 1 and the reverse brake 3. Each of the accumulators 13 and 15 acts to absorb shock occurring by the engagement of the forward clutch 1 and the reverse brake 3 respectively.
However, a complicated structure results in the conventional forward/reverse control system with the use of all these elements, that is the N-D control valve, the N-R control valve, the forward clutch accumulator, and the reverse brake accumulator.
The present invention has been made in an effort to solve the above problems.
It is an object of the present invention to provide a forward/reverse control system for a continuously variable transmission, in which an N-D control valve, an N-R control valve, a forward clutch accumulator and a reverse brake accumulator are combined into a single unit to simplify a structure of a hydraulic circuit of the system.
To achieve the above object, the present invention provides a forward/reverse control system for a continuously variable transmission comprising pressure regulating means for regulating an inputted line pressure according to whether a forward or reverse state is required; a manual valve for selectively supplying and exhausting hydraulic pressure, which is supplied from the pressure regulating means, to and from a forward clutch and a reverse brake; and a check ball unit mounted between a forward hydraulic line and a reverse hydraulic line, which are connected respectively to the forward clutch and the reverse brake, the check ball unit operating to communicate the forward hydraulic line with an accumulator when hydraulic pressure acts on the forward clutch and operating to communicate the reverse hydraulic line with the accumulator when hydraulic pressure acts on the reverse brake.
According to a feature of the present invention, the pressure regulating means comprises a pressure regulating solenoid valve for regulating an inputted hydraulic pressure as a duty control pressure; and a pressure regulating valve controlled by the duty control pressure of the pressure regulating solenoid valve to regulate the line pressure and supply the regulated line pressure to the manual valve.
According to another feature of the present invention, the pressure regulating solenoid valve is a normal high type valve.
According to yet another feature of the present invention, the pressure regulating valve comprises a valve spool provided within the pressure regulating valve; an elastic member provided to one side of the valve spool to exert a biasing force thereon; a first port to which the hydraulic pressure supplied to the pressure regulating solenoid valve is supplied, the first port being provided at an opposite side of the pressure regulating valve from the elastic member; a second port to which the duty control pressure of the pressure regulating solenoid valve is supplied to oppose the hydraulic pressure supplied to the first port and control the valve spool; a third port to which the line pressure is supplied; and a fourth port communicating with the third port to enable regulation of the line pressure by control of the valve spool, the valve spool being controlled by the elastic member and the hydraulic pressure supplied to the first and second ports, the fourth port also supplying the regulated line pressure to the manual valve.